The objective of this investigation is the radiobiological characterization of tumor cell populations separated and isolated from solid tumors and metastasis. This study will focus on both intra as well as inter variations in tumor response. Following exposure either in vitro or in situ to radiation alone or in combination with other modalities, selected tumor cell subpopulations will be removed and isolated by biophysical methods. Their responses will be determined and compared to the response of the tumor as a whole. The tumor systems that will be studied include: a methylcholanthrene-induced fibrosarcoma (FSa) and its in vitro growing clone, FSA 1233, a spontaneously arisen fibrosarcoma capable of forming spontaneous metastasis (NFSa), an L-P59 sarcoma, and a spontaneously arisen mammary carcinoma. The cell separation methods used include the separation of cells on the basis of their buoyant densities by means of centrifugation on linear density gradients of either Renografin or Percoll, and on the basis of their size by means of centrifugal elutration. Cell clonogenicity will be assayed in vivo using a lung colony assay and in vitro using standard tissue culture methods. Each of the separated tumor populations will be characterized with respect to selected biological parameters using biochemical assays, isotope labeling procedures, and flow microfluorometry in order to better understand its previous environmental situation within the tumor. In particular, individual separated cell populations will be studied following either in situ or in vitro exposure to determine: a) response to radiation sensitizing electron-affinic drugs; b) response to hyperthermia; c) ability to repair potentially lethal damage; and d) age response to radiation alone or in combination with other therapuetic agents. These results will be interpreted in relation to generating optimizing therapeutic protocols.